Alarm Bradycardia in White-Tailed Deer Fawns (Odocoileus virginianus)

Heart rates of five unrestrained white-tailed deer fawns (Odocoileus virginianus) were telemetered during prone behavioral responses ("freezing") to a variety of alarm stimuli. Decreases in heart rates, termed alarm bradycardia episodes, were significant and averaged 38% (range 11-68) below pre-bradycardia heart rates measured during lying-resting behavior in the unalarmed fawn. Episodes of alarm bradycardia (lasting from 5 to 111 s) were most frequent during the first week of life, when the concealment discipline was strongest, but decreased rapidly with growth. Heavier fawns may be further along a continuum of neuromuscular development and associated capacities for "fight and flight" responses, and are less likely to react to disturbances with prone responses and associated bradycardia than lighter fawns of similar age.